/Engine/Source/Runtime/Experimental/Iris/Core/Public/Iris/DataStream/DataStream.h
Called before any calls to potential WriteData, if it returns EWriteData::NoData no other calls will be made. The purpose of the method is to enable a DataStream to setup data that can persist over multiple calls to WriteData if bandwidth allows.
virtual [EWriteResult](API\Runtime\IrisCore\Iris\DataStream\UDataStream\EWriteResult) BeginWrite()